This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the presently described embodiments. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present embodiments. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Drilling and production operations for the recovery of offshore deposits of crude oil and natural gas are taking place in deeper and deeper waters. Drilling and production operations in deeper waters are typically carried out from floating vessels rather than from stationary platforms resting on the ocean floor and commonly used in shallow water. According to conventional procedures, a vessel is dynamically stationed, or moored, above a well site on the ocean floor. After a wellhead has been established, a blowout preventer (“BOP”) stack is mounted on the wellhead to control the pressure in the wellhead. After drilling is completed, a production tree is mounted on the wellhead to control produced fluids.
Subsea well boreholes are typically drilled with multiple sections having decreasing diameters as the wellbore extends deeper into the earth. Each borehole is cased with a casing string that extends into the borehole from a wellhead and is cemented within the borehole. The drilling, casing installation, and cementing are performed through one or more drilling risers that extend from the wellhead to the surface, such as to a floating drilling vessel. After drilling operations are completed, i.e., during production operations, produced fluids may travel to the surface through one or more production risers that extend from the wellhead to the surface.
Risers comprise a series of riser joints. Each riser joint includes flanges on each end of the joint. The flanges of one joint are made up, or bolted together, with the flange of an adjacent joint. In this way, a riser string is formed extending from the surface to the wellhead at the sea floor. The flanged connections between adjacent riser joints must contain the internal pressure of the riser string and must withstand large external loads experienced as a result of environmental conditions, i.e., the weight of the riser string and its movement in a body of water.
Traditionally, flanges are designed with raised face diameters inside the bolt circle. When made up, this design creates a highly localized preload near the flange inner diameter where elastomeric or metal-to-metal bore seals are located. This high preload is necessary to prevent flange face separation at the inner diameter, which would result in loss of bore seal integrity. The high preload is taxing on the riser flanges. Accordingly, an improved riser flange design which eliminates the need for high preload stresses encountered by existing designs is desirable.